1. Technical Background
The present invention generally relates to a balloon catheter for conducting dilatation procedures within the vascular system. The balloon catheter may be used in conjunction with a guiding catheter, within which the balloon catheter is slidably moved for positioning and treatment. The balloon catheter includes an elongated, high-strength cannula or hypotube as a proximal tube component. The catheter has a distal end assembly which includes the balloon and which has a substantially greater flexibility than that of the proximal cannula. The proximal cannula and the distal end assembly are joined together by a transition assembly which has a stiffening element. The present invention improves various performance features of the catheter, including trackability, pushability, flexibility, etc.
2. Discussion
In many applications for dilatation catheters, it is desirable to provide a proximal catheter tube which is relatively stiff and of high strength so that the elongated proximal tube accepts and transmits column force, as well as torsional forces, from the proximal end of the catheter which remains outside of the body, to the distal end portion of the catheter so that the balloon is properly positioned for performing the dilatation procedure.
Proximal elongated tubes such as metal hypotubes have been proposed or used in the past for balloon catheter shafts. However, this type of stiff tubing preferably does not extend the full length of the balloon catheter. In order to maneuver through tight turns and/or constricting passageways, the distal end portion of the catheter should be quite flexible.
While having a stiff proximal hypotube and a flexible distal portion has been a desirable objective, achieving this objective is complicated by the need for providing a suitable transition between a relatively stiff elongated member and a relatively flexible elongated member. As used in this patent, the term xe2x80x9celongatedxe2x80x9d refers simply to having a measurable length, as opposed to implying any stretching or process that might otherwise be considered xe2x80x9celongationxe2x80x9d. It has been found that, when two such diverse stiffness sections interface directly with each other, there is a tendency that the catheter may kink or prolapse on itself during movement of the balloon catheter with respect to the guiding catheter. Accordingly, the balloon catheter may not move consistently and smoothly through the guiding catheter, or even reach the desired site. At times, the guiding catheter may dislodge from its desired position within the vascular system of the body.
In the past, catheters of this general type have included a transitional section between a stiff hypotube type of component and a flexible distal end portion of the catheter. A primary component of these types of transitional section approaches is the incorporation of a structure having selected flexibility or range of flexibilities generally at the transition location, whereby the stiffness at the proximal hypotube is gradually reduced toward the flexible distal portion of the catheter. In some known systems, a bridging wire is attached to the hypotube as a distally oriented extension of the hypotube, positioned within a transition section between the hypotube distal end and the distal portion of the catheter with the balloon.
With approaches such as those generally identified above, the bridge wire or a similar structure may present challenges when the balloon catheter must be passed through a tightly curved portion of the guiding catheter. There may be a tendency for the bridge wire to transfer a bending or lateral force to the walls of the guiding catheter, due to the stiffness of the bridging wire, which lateral force typically increases when the tightness of the curve increases.
It is accordingly desirable for a catheter system to have a balloon catheter which will easily navigate tight curves in the distal portion of the guiding catheter without imparting undue lateral force to the walls of the guiding catheter, which could possibly result in unintentional dislodgement of the guiding catheter due to movement of the balloon catheter. Accordingly, the present invention concentrates on the structure of a transition section between a relatively stiff proximal tube and a relatively flexible distal portion.
The present invention can also be relevant in catheters having a rapid exchange configuration, which incorporate a guidewire lumen only at a distal end portion of the catheter. Such an overall structure permits the physician to easily and rapidly exchange one balloon catheter for another, and generally avoids the need for extended or extendable length guidewires, and the issues associated with providing and handling them. Balloon catheter systems of this general type are shown in Yock U.S. Pat. No. 5,061,273 and Leopold U.S. Pat. No. 5,346,505, and their subject matter is incorporated herein by reference. Generally, by providing a guidewire exit port in a generally distal portion of the catheter, it can intensify the possibility of undesired weakness or sharp flexibility transitions of the catheter. Such weakness may be caused by abrupt flexibility differences between a distal section of the catheter having the guidewire tube and guidewire, and a proximal section of the catheter immediately proximal of the guidewire exit port. There is accordingly a preference for an improved transition structure in balloon catheters generally, and in the vicinity of the guidewire exit port of balloon catheters having a rapid exchange configuration.
In accordance with the present invention, a balloon dilatation catheter has an improved transition assembly between a relatively high-strength proximal cannula and a generally tubular distal end assembly, which is substantially more flexible than the proximal cannula. The transition assembly provides flexible bending strain relief having optimized flexibility, column strength, pull strength, and other characteristics. The transition assembly preferably includes a stiffening member within a transition tube. Moreover, the stiffening member may preferably be attached to the catheter shaft near its distal end, and float relatively freely in the catheter shaft at its proximal end.
This balloon dilatation catheter will often be used in combination with a guiding catheter, so the balloon dilatation catheter is able to smoothly follow sharp curves of the guiding catheter which may be encountered during a dilatation procedure such as angioplasty. With this combination, the transition assembly is optimized to impart a minimal lateral force on the guiding catheter, so as to avoid dislodgement of the guiding catheter from its intended position in the vascular system, as the dilatation catheter is moved within the guiding catheter.
Accordingly, a general possible object of the present invention is to provide an improved balloon dilatation catheter, combination of dilatation catheter and guiding catheter, and method for making the balloon dilatation catheter.
Another possible object of this invention is to provide an improved balloon catheter having a transition assembly which provides flexible bending strain relief during medical procedures.
Another possible object of the present invention is to provide an improved combination of balloon dilatation catheter and guiding catheter, such that during slidable positioning of the balloon dilatation catheter within the guiding catheter, the transition section readily bends in an arc, thereby minimizing the lateral force applied to the guiding catheter and avoiding dislodgement of the guiding catheter from the desired position.
Another possible object of this invention is to provide a balloon dilatation catheter which moves linearly in the distal direction inside of a guiding catheter, without undesired flexing of the transition assembly, which could hinder transmission of forces from the proximal end of the catheter outside the body to the distal end of the catheter inside the patient""s body.
Another possible object of the present invention is to provide an improved balloon dilatation catheter and guiding catheter combination, which reduces the chance of having the guiding catheter become dislodged from the desired position during an angioplasty procedure.
Another possible object of this invention is to provide a balloon dilatation catheter having a transition section which reduces the incidence of kinking the catheter.
Another possible object of the present invention is to provide an improved balloon dilatation catheter and guiding catheter combination, which exhibits an advantageous ease of tracking and lower tracking force, due to having an improved transition section which forms to the shape of the guiding catheter when that transition section moves through the guiding catheter.
Another possible object of the present invention is to provide a transition section for a balloon dilatation catheter which provides a relatively larger cross-sectional area for passage of balloon inflation fluid during balloon inflation and deflation.
These and other possible objects, features and advantages of the present invention will be apparent from and clearly understood through a consideration of the following detailed description of the preferred embodiment.